Our research is concerned with the nature of avian retrovirus gene expression and the manner in which translational and post-translational events act to control virus multiplication. We are currently involved in several projects focused on expression of endogenous retrovirus genes present in normal uninfected cells and on the synthesis and assembly of viral polyproteins into virions: 1. Viral gene expression in normal uninfected cells: we are engaged in a study of a major endogenous virus genetic locus which, although ordinarily silent, can be induced to produce a defective virus particle. The mechanism of gene activation and the nature of the defect in this virus are being studied. 2. Packaging of endogenous retrovirus in RNA into virions: we have found that exogenous avian sarcoma viruses package into virions relatively high levels of an endogenous viral mRNA. We are attempting to determine whether this mRNA can be reverse transcribed and stably integrated into newly infected cells. 3. Membrane induced cleavage of the gag precursor polyprotein: we have found that membrane fractions from uninfected cells can induce what is probably the first cleavage event in the gag precursor. The identification of the protease responsible is currently underway.